U.S. Pat. No. 6,394,465 discloses a tool clamping device including a clamping member having an insertion bore formed by the union of an access bore portion and a gripping bore portion. An insertion member having a cylindrical shank portion with a diameter smaller than the access bore portion diameter, is insertable into the access bore. The diameter of the shank portion is slightly larger than the diameter of the gripping bore portion. When the clamping mechanism is transferred to a clamped position, the insertion member is forcibly fitted into the gripping bore portion by an external force exerted on the shank portion by a bearing sleeve or a clamping screw. A firm clamping between the shank portion and the gripping bore portion is maintained by the external force. The external force guarantees that the shank portion remains pressed against the gripping bore portion during operation of the cutting tool. Without the external additional force, the clamping mechanism of '465 cannot perform as such, since any external force applied on the gripped shank portion, in a direction transverse to a longitudinal direction of the shank portion, may pull the shank portion out of the gripping bore portion.
In the clamping method where the clamping screw is used to force the shank portion into the gripping bore portion, the wall into which the clamping screw is threaded, must have a minimum thickness, in order for the thread to work properly.